Optical fiber is a common transmission medium for telecommunications. It is especially advantageous for long distance communications because light propagates through the fiber with little attenuation as compared to electrical cables and because higher data rates are possible.
In most long distance communication applications, single mode optical fiber is used. However, the use of multimode optical fiber or few mode optical fiber can provide higher information capacity than using single mode optical fiber through a mode division multiplexing technique. Few mode fiber, by definition, is designed to support multiple guided modes at a given wavelength. Each mode can be used to transmit independent optical channels therefore increasing the total capacity by a factor of N, where N is the number of modes supported by the few mode fiber.
Although the ability to support multiple guided modes could be used to transmit more data, few mode fiber can suffer from distortion issues which become particularly problematic over longer distances. For example, fiber imperfections, such as index inhomogeneity and bends, may cause coupling between modes. As a result of mode coupling, a light pulse launched into a single mode couples to other modes, which leads to a superposition of several pulses at the fiber output and causes interference and a reduction of fiber bandwidth.
Coherent detection and computationally intensive multiple input multiple output (MIMO) digital signal processing (DSP) have been utilized to mitigate these distortion issues. However, utilization of such techniques increases the complexity of the components of the data transmission system, which in turn leads to reductions in energy efficiency and increases the costs associated with the system.